The present invention relates generally to medical devices for forming holes in heart chamber interior walls in percutaneous myocardial revascularization (PMR) procedures. More specifically, the present invention relates to intravascular PMR devices having expandable baskets deployable within heart chambers.
A number of techniques are available for treating cardiovascular disease such as cardiovascular by-pass surgery, coronary angioplasty, laser angioplasty and atherectomy. These techniques are generally applied to by-pass or open lesions in coronary vessels to restore and increase blood flow to the heart muscle. In some patients, the number of lesions are so great, or the location so remote in the patient vasculature that restoring blood flow to the heart muscle is difficult. Percutaneous myocardial revascularization (PMR) has been developed as an alternative to these techniques which are directed at by-passing or removing lesions.
Heart muscle may be classified as healthy, hibernating and xe2x80x9cdeadxe2x80x9d. Dead tissue is not dead but is scarred, not contracting, and no longer capable of contracting even if it were supplied adequately with blood. Hibernating tissue is not contracting muscle tissue but is capable of contracting, should it be adequately re-supplied with blood. PMR is performed by boring channels directly into the myocardium of the heart.
PMR was inspired in part by observations that reptilian hearts muscle is supplied primarily by blood perfusing directly from within heart chambers to the heart muscle. This contrasts with the human heart, which is supplied by coronary vessels receiving blood from the aorta. Positive results have been demonstrated in some human patients receiving PMR treatments. These results are believed to be caused in part by blood flowing from within a heart chamber through patent channels formed by PMR to the myocardial tissue. Suitable PMR holes have been burned by laser, cut by mechanical means, and burned by radio frequency current devices. Increased blood flow to the myocardium is also believed to be caused in part by the healing response to wound formation. Specifically, the formation of new blood vessels is believed to occur in response to the newly created wound.
What would be desirable is a device capable of forming multiple holes in the wall of a heart chamber but requiring minimal manipulation while positioned within the chamber. What would be desirable is a device capable of forming multiple holes in a short time period in the myocardium.
The present invention provides devices and methods for forming a plurality of holes in a heart chamber wall as part of a percutaneous myocardial revascularization (PMR) treatment. Devices according to the present invention have a basket, termed a PMR basket, formed of a plurality of arcuately biased flexible arms. The arms can assume an outwardly bowed configuration once freed of the confines of a shaft lumen. The fully deployed PMR basket arms can expand until the arms engage the walls of the heart chamber. Some devices provide for multiple, simultaneous myocardial hole formation. In such devices, cutting means such as RF electrodes are carried on the arms and disposed outwardly to engage the heart chamber walls. The term xe2x80x9ccuttingxe2x80x9d as used herein, means penetration, including the formation of holes by burning and by other means. One device utilizes a PMR basket to anchor or stabilize a steerable PMR cutting probe within the heart chamber.
The present invention provides devices and methods for forming numerous holes in a heart chamber wall within a short time period. This reduces the amount of time the heart chamber is invaded by the foreign device. Some devices and methods according to the present invention allow for the formation of many holes while requiring minimal maneuvering once the devices are advanced into the heart chamber.
One group of PMR basket devices includes an elongate outer tubular shaft having a lumen, a proximal end and a distal end. A plurality of elongate flexible arms are secured together at their proximal and distal ends, the arms being biased so as to bow outward relative to an axis through the secured proximal and distal ends. The arms carry a plurality of cutting means disposed in an outward direction toward the chamber wall. One device arms have lumens therethrough and outwardly oriented apertures. This device includes electrical supply wires running though the arms lumens and electrode wires extending from the supply wires and through the arm apertures. This device can include arcuately biased electrode wires that can be formed of a shape memory material. The biased arms can extend radially outward away from the arm when unconstrained, especially when heated by body fluids. One device includes a single supply wire slidably disposed within the arm lumen and electrically connected to each of the electrode wires which are slidably disposed within an arm aperture. The electrode wires can be advanced away from the apertures by advancing the supply wire within the arm. A variation of this embodiment utilizes cutting probes having sharpened free ends capable of piercing the heart chamber wall and forming holes within the myocardium.
In another embodiment of the PMR basket, the basket includes a plurality of electrode groupings. The electrodes can also have a loop shape, which can be, for example, semi-circular. Both the electrode grouping and loop shaped electrodes can be used to form craters in the myocardium of a patient""s heart rather than channels. Craters can be considered wounds which have a width greater than their depth, whereas channels can be considered to a have a depth greater than their width. A hole is the resulting space after volumetric removal of material has been made from the patient""s heart wall. A hole can be either a crater or a channel. It is believed that forming craters, in some instances, provide better therapeutic value than forming channels in the myocardium as their formation can be better controlled to reduce the likelihood of heart wall perforation.